SSL devices generally use semiconductor light emitting diodes (LEDs), organic light-emitting diodes (OLED), and/or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, a plasma, or a gas. FIG. 1A is a cross-sectional diagram of a portion of a conventional indium-gallium nitride (InGaN) LED 10. As shown in FIG. 1A, the LED 10 includes a silicon substrate 12, an N-type gallium nitride (GaN) material 14, an InGaN material 16 (and/or InGaN/GaN multiple quantum wells), and a P-type GaN material 18 on one another in series. The LED 10 also includes a first contact 20 on the P-type GaN material 18 and a second contact 22 on the N-type GaN material 14.
One drawback of the LED 10 in FIG. 1A is that the thermal expansion coefficients (TECs) between GaN/InGaN materials 14, 16, and 18 and the silicon substrate 12 are different and may cause the LED 10 to bow and/or otherwise flex under thermal stress. Such bowing or flexing can cause the GaN/InGaN materials 14, 16, and 18 of the LED 10 to crack and/or have other structural defects.
Another drawback of the LED 10 is that the silicon substrate 12 typically includes silicon wafers with a Si(1,1,1) lattice orientation instead of those with a Si(1,0,0) lattice orientation. FIG. 1B is a schematic perspective view of a portion of a silicon lattice illustrating both the Si(1,1,1) and Si(1,0,0) lattice orientations. It is believed that the epitaxial growth of the GaN/InGaN materials 14, 16, and 18 prefers a hexagonal lattice structure provided by the Si(1,1,1) wafers. However, Si(1,1,1) wafers are more expensive than commonly available Si(1,0,0) wafers. Accordingly, several improvements in reliably and cost-effectively manufacturing LEDs may be desirable.